Plastic cable ties have become increasingly popular for a variety of bundling and attachment applications because of their relatively low initial cost and their ease of installation. However, in addition to unsuitable aging characteristics, plastic ties tend to become brittle when used at low temperatures and, when used in a high temperature, high humidity environment, tend to undergo some elongation. Moreover, plastic ties are inappropriate for certain nuclear power plant applications since radiation can result in degradation of the plastic material thereby rendering the strap more brittle. Therefore, in certain applications, it is more desirable to use a metallic cable tie. For instance, metal ties are often used in underground, corrosive, nuclear and heavy vibration environments and in situations where it is desired to use the tie as a load carrying member since the metal tie typically has a much greater tensile strength than plastic ties.
In response to drawbacks associated with using plastic cable ties in harsh environments, the industry has seen some use of metal cable ties, some of which were initially designed typically on the same principle as plastic ties. While these designs are suitable for their intended purpose, they too suffer however from requiring a very high insertion force of the strap through the head of the tie. In order to reduce the high insertion force, some metal designs have been modified to utilize a roller means in the form of either a sphere or cylindrical pin within the head for lockingly engaging the strap. These types of metallic cable ties, generally known as "ball-lock" or "roller-lock" cable ties, proved to be successful in decreasing the insertion force. In certain environments such as a heavy vibration environments, however, the locking of the strap in the head of these cable ties may become loose due to partial unwedging of the ball or pin in the head which allows retrograde movement of the strap (i.e., the strap becomes loose). This "loose fit" condition results because metal, such as steel, does not stretch during installation (i.e., does not have any noticeable elongation or memory such as plastic), thus no back force to prevent or counteract retrograde movement of the strap is present to maintain the ball or pin in the locked or wedged position.
In view of the foregoing, a need exists for a cable tie which has a means for preventing retrograde movement of the strap from its locked position and for taking up slack and maintaining tension on the strap as well as ensuring locking of the ball or pin inside the head of the tie.